Apparatus for railway train communication systems



May 12, 1936. P. N. BossART 2,040,198

4 APPARATUSFOR RAILWAY TRAIN COMMUNICATION SYSTEMS Filed July 26, 1934 gigorrfgal {Communieazz'ny 16'. 1 A I I 1%? E21 5 Hfi 28 F025 l I 27 Receiving 40 f 39 figgfi 6 54 45 55 F'lz F1 L e V RA Code M21220 1.0

O 7400 7600 7500 8000 8200 8400 0000 (9,900 0000 Frequency Fig.2

INVENTOR PaulMBossam dim LL00 HIS ATTORNEY Patented May 12, 1936 UNITED STATES PATENT OFFICE APPARATUS FOR RAILWAY TRAIN COMMUNICATION SYSTEMS Application July 26, 1934, Serial No. 737,076

12 Claims.

My invention relates to apparatus for railway train communication systems, and particularly to apparatus for carrier telephone systems for railway trains in which a frequency equal to the carrier modulated by a predetermined voice frequency is used for calling and code communication.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in claims.

A feature of my invention is the provision in systems of the type here involved of train-carried low-power factor inductors which for telephone communications are tuned to resonance at different frequencies within the voice spectrum, the resonant frequency of the different inductors being frequencies which differ from each other, and one-half of which inductors are: reversed with respect to the other half with the result that an advantageous addition of energy throughout the voice spectrum will be obtained, and. the frequencies at the band edges of the voice spectrum will be transmitted and received at an energy level not greatly less than the energy level of the mid-frequencies, at least the variation in strength betweenthe frequencies at the band edges and the mid-frequencies will be within the limits necessary to assure readily intelligible speech. For calling and code communication the inductors are each sharply tuned to resonance at the predetermined calling frequency, with the result that noise and unwanted energy Will be suppressed to a low level and a considerable gain in the: power transfer of the desired energy will be obtained.

In other words, for telephone communication the tuning of the different inductors is staggered along the voice spectrum. Staggered tuning, when referred to in the following description, will, therefore, be understood to mean tuning the different inductors and circuits therefor to resonance at different frequencies-spaced apart within the band it is desired to transmit. For calling and code communication the different inductors are each sharply tuned to thesame frequency.

Apparatus for using the traflic rails as a communication channel is disclosed in a copending application, Serial No. 450,135, filed May 6, 1930, by L. O. Grondahl, for Electric train signaling systems. Switching apparatus set-forth in my present application to effectively transfer the communication channel between the transmitting and the receiving apparatus is somewhat similar to the apparatus set forthin the copending application for Communication systems, Serial No.

31 729,806, filed June 9, 1934, by L. D. Whitelock et a1; and in my copending application, Serial No. 72,605, filed April 3, 1936, for Railway train communication systems. The present application may be considered an improvement on the above cited copending applications. 5

For a better understanding of my invention reference may be had to the accompanying drawing in which Fig. 1 is a diagrammatic view of one form. of apparatus embodying my invention. Fig.

2 is a diagram of certain characteristic curves of the apparatus of Fig. 1.

Systems have been proposed for communication from a station located on a vehicle of a railway train with a wayside station or with a station located on the vehicle of another train or with another station located on a second vehicle of the same train by transmitting between the two stations a carrier current modulated with voice frequencies for telephoning, and by transmitting a frequency equal to such carrier modulated by a predetermined voice frequency for calling and code signaling. In such systems heretofore proposed a station in sending out such current supplies the current to the trafiic rails of the track occupied by the train through the medium of a circuit electrically coupled with the traffic rails, the current flowing in both directions from the point it is supplied to the rails and returning through the ground. Current'is picked up at the receiving station through the medium of a circuit electrically coupled with the trafiic rails. In such systems the receiving apparatus at each station is normally active and in circuit ready to receive a message from the remote station at any time, but the transmitting apparatus at each station is normally inactive and is energized and placed in circuit only during the sending of current from that station. The receiving apparatus preferably includes a high gain amplifier and a loud speaker, and since it is normally in circuit small earth currents and stray magnetic fields picked up during non-communicating periods may produce a noise that sometimes becomes very annoying. It has been proposed to normally tune the receiving circuit sharply to a single frequency which corresponds to the calling frequency of the companion station so that noise currents and unwanted energy of only a few cycles will be efi'ective to create voltages of operative magnitude in the receiving circuit and noise will be reduced 5 to a low level, but impulses of current of the proper calling frequency will be effective to create voltages in the receiving circuit that are operative to produce a relatively strong signal. The tuning of the receiving circuit is broadened for the rein accordance with the prearranged code, the receiving circuit at the remote station being retained at its sharply tuned condition. To fix the ideas, I shall assume that a band of voice frequencies extending from 600 cycles to 1800 cycles per second for telephoning is desired, the calling frequency is 800 cycles per second, a carrier of 7000 cycles per second is employed, and that single side band transmission is contemplated, the upper side band being utilized. It follows that during telephone communication a band of frequencies extending from 7600 to 8800 will be transmitted and for calling and code communication the frequency will be 7800 cycles. It will be understood, of course, that my invention is not limited to these specific frequencies and other frequencies may be chosen if found desirable.

It will be apparent that a sharply tuned circuit effective to receive a single calling frequency will be equally efiicient for sending a like current by switching the circuit from the receiving apparatus to the transmitting apparatus and su plying current thereto. Likewise, when such a circuit is set for reception of a telephone current, it may be employed in sending out such telephone current by switching the circuit to the transmitting apparatus and supplying a telephone current thereto. Furthermore, such a circuit when set .for telephone communication will also be responsive to current of the calling frequency since the calling frequency lies within the band employed for telephone communication.

The transmitting apparatus for such systems ordinarily includes a microphone, a generator of carrier current, means for modulating thecarrier with frequencies corresponding to the voice impulses produced in th microphone, calling means operative to produce a frequency equal to the car'- rier modulated by a predetermined voice frequency and an amplifier for amplifying the outgoing current to a relatively high energy level. The receiving apparatus will ordinarily include in addition to the high gain amplifier and loud speaker referred to: above, a demodulator for reproducing the audio frequencies of the modulated carrier, an audio frequency amplifier and filters for suppressing frequencies outside the desired band. The specific structure for such amplifiers, modulators and demodulators forms no part of nm present invention and these devices will be referred to in the. present description only insofar as it is necessary for an understanding of my invention.

Referring to Fig. 1, the microphone of the transmitting apparatus is indicated by the reference character M, while the carrier generator, modulator, calling current generator and transmitting amplifier are indicated conventionally at TA, since, as stated above, these latter devices form no part of my present invention and may take any of several forms well known to the art. The microphone M is preferably carried during non-communicating periods in-a rack not shown and out of which it may be lifted when it is desired to establish a telephone conversation in order that it may be brought close to the person speaking. To facilitate the handling of the microphone M it is mounted on a handle l5 which is adaptable to be manually operated to any one of three positions which I shall term normal, communicating and calling, these three positions being indicated by dotted lines in the drawing. As shown schematically, two circuit controlling contacts I6 and 6| are operatively connected with the handle [5 and are moved to the three positions designated by the numerals l, 2 and 3 in response to the normal, communicating and calling positions, respectively. A push button I! is also mounted on the handle I5, the contact member 18 of. which is adapted to make engagement with a contact l9 when the push button is depressed and to break engagement therewith when the push button is released. A circuit controlling contact 20 is associated with the microphone M and biased by its own spring action to make engagement with a stationary contact 2| but is normally held out of engagement therewith through the medium of an insulated member 22 mounted on the microphone M, the arrangement being such that with the microphone M placed in the rack the member 22 forces the.

spring 20 to the left in the drawing and out of.

engagement with the contact 2|, but that with the microphone M removedfrom the rack, thatcomplete the connection therethrough. It will.

be noted that the handle I5 may be operated to any one of its three positions with the microphone remaining in the rack, as well as when it is lifted out of the rack.

The microphone. M'is connected with the input of the apparatus TA over wires l0 and I I, while wires l2and l3 connect the output of the apparatus TA with the winding M of 'a transformer T, a front contact 59-60 of a directional relay DR to be. referred to later being interposed in the wire I2. The circuit for rendering the calling apparatus active. to supply a calling frequency current is shown completed by the contact 6| being moved to its No. 3 position to connect the two wires 62 and 63. It is deemed sufficient for this description to say that frequencies corresponding to voice frequencies developed in the microphone will be applied to the carrier, which in this instance is of 7000 cycles per second, for modlevel and supplied to the winding 14 of the transformer T, the winding l4 being in turn effective to induce electromotive forces ofcorresponding frequencies in transmitting circuits to be. described more fully hereinafter. Completing the connection between the wires 62 and 63 by operating the. handle l5 to the calling position to move the contact 6| to its No. 3 position will cause the apparatus TA to produce acalling or code frequency current which in this instance is of- 7800 cycles per second and which current will be amplified to a relatively high energy level and supplied to the winding l4 and in turn supplied to the transmitting circuits.

The equipment of Fig. 1 includes a directional relay DR and a tuning relay R. both of which are shown as direct current neutral relays adaptable of being energized by direct current from any convenient source as a battery not shown. The directional relay DR is providedwith two energizing circuits both of which are easily traced and one of which includes the No. 2 position of the contact I6 and the push button I! depressed, and the other of which includes the No. 3 position of the contact l6 only. That is to say, the directional relay is deenergized under the normal position of the microphone'handle l5, and is energized when the handle I 5 is moved to the communicating position and. the push button I! is depressed, and also when the handle 15 is moved to the calling position. The tuning relay R is provided with two simple energizing circuits one of which includes the contact 20-2l and the other of which includes the contact 23 of a common spring return push button 24. Hence, the tuning relay R is normally deenergized and is energized whenever the microphone M is taken out of the rack and the contact 202l is closed, and may also be energized while the microphone M remains in the rack by the depressing of the push button 24. The function of the tuning relay R and the directional relay DR will appear later in the description. I

Cl and C2 of Fig. 1 are inductors mounted on the vehicle of a train on which a station is to be established. These inductors CI and C2 may take different forms and are here shown as air core coils of relatively large central area and constructed to have a relatively low power factor of say 0.5% at frequencies of the order of 10,000

cycles per second. While inductors Cl and C2 are here illustrated as coils consisting of a plurality of turns, it will be understood that they may consist of many or only a fraction of a .iiturn as desired. Furthermore, other forms of low power factor inductors may be employed if found desirable to do so.

Referring first to the inductor Cl, a circuit can be traced from the. lower terminal of the inductor over a back contact 25-26 of the tuning relay R, condenser 21, the lower portion of a winding 28 of the transformer T and wire 29 to the upper terminal of the inductor. The condenser 21 and the lower portion of the winding 28 are so proportioned and adjusted that this circuit is tuned to resonance at the frequency of the calling or code current, namely at 7800 cycles per second. Furthermore, the parts of this circuit are so proportioned that the circuit power, factor is say, about 1.0%, which, with the 0.5%

power factor for the coil Cl allows approximately a maximum transfer of energy. With the relay R picked up to open the back contact 25-26 and to close a front contact 2530 the coil CI is included in a circuit extending from the lower terminal of the coil Cl over front contact 25--30 of relay R, condenser 3l, winding 28 and wire 29 to the upper terminal of coil CI. The condenser 3| is so proportioned as to tune this second circuit for the coil CI to resonance at say 8600 cycles per second, that is, at a speech frequency corresponding to the carrier of 7000 cycles modulated at the voice frequency of 1600 cycles. In other words, this second circuit is tuned to resonance at a frequency near the upper edge of the voice spectrum. The winding 28 is so constructed as to increase the circuit resistance sufficiently to raise the circuit power factor to a value, say, of 3.25%. The coil C2 is normally in circuit with the lower portion of a Winding 32 of the transformer T, the circuit including a back contact 33-34 of the relay R and a condenser 35. The parts of this circuit for the coil C2 are so proportioned and adjusted as to tune the circuit to resonance of the frequency of the calling current and to establish a circuit power factor of about 1.0%; When the relay R is picked up, the coil C2 is transferred to the top portion of the winding 32, the connection being completed at the front contact 3358 of the relay R, the condenser 35 remaining in the circuit. The top portion of the winding 32 is so constructed and wound that this second circuit for the coil C2 remains tuned to resonance at the frequency of 7800 cycles but the resistance of the circuit is increased and the power factor of the circuit is raised to say 3.25%. The lower terminal of the coil C2 being connected with the mid-terminal of the winding 32 and the top terminal of the coil C2 being connected with the bottom terminal of the winding 32 when the relay R is deenergized and with the topterminal of that winding when the relay R is picked up, it is clear that the direction of the flow of current supplied by the coil C2 to the winding 32 when the relay R is released is reverse to the direction of the flow of current supplied to the winding when the relay is picked up. It is to be noted that the connection of the coil Cl with the winding 28 is such under the two different positions of the tuning relay R the current flows in that Winding in the same direction under both positions of relay. It is to be seen, therefore, that with the tuning relay released the circuits including the two coils CI and C2 are both tuned to resonance at the calling frequency of 7800 cycles per second, the power factor of each circuit is about 1.0% and the currents supplied to the two windings 28 and 32 are in phase. When the relay R is picked up, the circuit including the winding Cl is tuned to resonance at 8600 cycles near the upper edge of the voice spectrum, the circuit including the coil C2 is tuned to resonance at 7800 cycles near the lower edge of the voice spectrum, the power factor of each circuit is now about 3.25%, and the connection of the coil Cl with the Winding 32 is reversed. It follows that under the deenergized position of the tuning relay the electromotive forces induced in the winding 36 of the transformer T in response to the currents supplied to the two windings 28 and 32 are in phase and add their effects, but that with the relay R picked up, the electromo tive forces induced in the winding 36 in response to the currents supplied to the two windings 28 and 32 have a phase difference. The results to be accomplished by this arrangement of tuning, power factorsand phase relationship of the coils Cl and. C2 will shortly appear. I The electromotive forces induced in the winding 36 of the transformer T are supplied to the receiving apparatus through an input filter which in this instance is inserted into the connection during telephone reception for suppressing frequencies outside of the voice spectrum and most of which filter is taken out of the connection for calling and code reception. The winding 36 is connected over wires 31 and 38 with the input side of the filter which is designated as a whole by the reference character Fl, a back contact 40-39 of the directional relay DR being interposed in the wire 3'1. The output reactor 4| of the filter Fl is included in the input of the receiving apparatus RA, which apparatus as previously stated will preferably include a high frequency amplifier, a demodulator and an audiofrequency amplifier, the final signal being in turn supplied to a loud-speaker LS. It is deemed sufficient for this application to point out that a telephone current of the side band range of 7600 to the input of the apparatus RA, it will be amplified, demodulated and a current of 800 cycles will be supplied to the loud-speaker to sound a corresponding tone.- In the event a current of 7800 cycles is coded in accordance with a p-rearranged code, tone notes corresponding to 800 cycles will be sounded by the loud-speaker in accordance with the prearranged code. The filter Fl may take different forms and as here shown comprises one section of a band-pass filter with infinite attenuation just below the voice band desired, say at 6800 cycles, and a half section with infinite attenuation at zero frequencies and at infinite frequencies. In this instance the filter Fl includes reactors 42, 43, M and 4|, and condensers 45, 06', 41, 48 and 49, two circuit controlling contacts R50 and R5! of the tuning relay R being also interposed in the circuit network. These relay contacts R50 and R5| are shown located within the filter Fl and remote from the winding of the relay R for the sake of simplicity, and it will be understood that with relay R released, contacts 50 and 5| make engagement with theback contacts 52 and 53, respectively, and that, with relay R energized, the contacts 50 and 5| are lifted out of engagement with their respective back contacts and into engagement with the front contacts 54 and 55, respectively.

At such time as both relays R and DR are released the winding 36 of the transformer T is connected with the receiving apparatus RA with most of the filter Fl out of the circuit, the connection being traced from the lower terminal of the winding 36 along wire 38, reactor 4|, wire 51, back contact 50-52 of relay R, wire 31, back contact -39 of the relay DR and the upper terminal of the winding 36, the reactor 4| being in turn connected with the apparatus RA. The two condensers 4B and 49 are connected in parallel across the reactor 4| to tune this circuit for the winding 36 to resonance at the calling frequency, and the parts of the circuit are so proportioned that the circuit will preferably have apower factor of about 4.0% at frequencies of the order of the calling frequency. At such time as the tuning relay R is picked up and its front contacts 54 and 5l55 are closed and the directional relay DR is released, the winding 36 is connected with the input of the receiving apparatus RA through the network of the filter Fl aswill be readily understood by an inspection of Fig. 3. Again, at such time as the directional relay DR is picked up and its back contact 4039 opened, the receiving apparatus RA is entirely disconnected from the winding 36 with the result that the receiving apparatus isinactive,

To sum up the apparatus of Fig. 1 thus far, when the directional relay DR is released for receiving and the tuning relay R is released, the coils Cl and C2 are included in 1.0% power factor circuits tuned-sharply at 7800 cycles, and through the transformer T and the circuit including reactor 4| supply energy to the receiving' apparatus the two currents supplied by the two coils being in phase. These 1.0% power factor circuits tuned to resonance at the frequency of the calling current will give an attenuation of about 150 to 1 at one-half frequency, that is, at about 4000 cycles and the 4.0% power factor circuit including reactor 4| will give about 5 to 1 attenuation at one-half frequency. Hence, the two receiving circuits together with the'circuit including the winding 36' and the reactor 4| will give an attenuation of several thousand at frequencies one-half of the calling frequency. Since most of the noise is at the lower frequencies and varies in amount inversely as the frequency, it follows that these receiving circuits will suppress noise to a low level and further filters will be unnecessary. Since the two low power factor circuits for coils Cl and C2 are in phase and the network of the filter Fl is mostly disconnected during calling and code reception, high pick-up sensitivity and a relatively large transfer of energy will be obtained. During periods the directional relay is released and the tuning relay is picked up, the

two coils Cl and C2 are each included in a 3.25% power factor circuit, which circuits are tuned to resonance at 8600 and 7800 cycles, respectively, the coils being reversed with respect to one another. This second arrangement of coils Cl and C2 will pass a relatively wide band of frequencies, and an advantageous addition of the received energy will be obtained.

As stated hereinbefore, a feature of my present invention is the provision of inductor coils which for telephone reception will provide an advantageous addition of the energy picked up, and the variation in strength between the frequencies at the band edges of the voice spectrum and the mid-frequencies will be within the limits necessary to insure readily intelligible speech, it having been found that this variation in strength should not be greater than 1 to 2. It remains now to show how two 3.25% power factor circuits with staggered tuning and reversed connections will cover the voice spectrum desired, namely, 7600 to 8800 cycles with a variation in current strength between the frequencies at the band edges and mid-frequencies which does not exceed the 1 to 2 ratio. I shall consider the strength of the resultant currents for the two pick-up circuits at the frequencies of 7600, 7800, 8000, 8200, 8400, 8600 and 8800 cycles, it being understood that the resultant current for frequencies between such cycles will approximate those selected. I shall further assume the current strength of the circuits for the two coils Cl and C2 at the resonant frequency to be equal to 1.0, that is, the maximum strength of the current picked up by either of the coils Cl and 02 will have the relative value of 1.0.

At the frequency of 7600 cycles, which is the lower edge of the voice spectrum, the current fiow in the circuit including the coil C2 will be about 0.53 of its maximum strength since it is tuned to resonance at 7800 cycles, and the current fiow in the circuit including the coil Cl will be less than 0.1 of its maximum strength since it is tuned to resonance at 8600 cycles. Furthermore, at the frequency of 7600 cycles the current of coil Cl will oppose that of coil C2 at about 30 degrees phase angle so that the combination or resultant current will be equivalent to 0.53-0.10 cos 30 degrees or equal to approximately 0.45 of the maximum value of the current of coil C2. Hence, the electromotive force induced in the winding 36 as the result of the two currents of the frequency of 7600 flowing in the windings 28 and 32 will have a relative value equal to that produced by a current of 0.45. At 7800 cycles, the current flowing in the circuit of coil C2 will be approximately at its maximum value of 1.0, but that produced in the circuit of the coil CI will only be about 0.1 of its maximum value, and

these two currents will be almost in quadrature.

Consequently, the effective electromotive force induced in the winding 36 will have a relative value equal to that produced by a current approximately equal to 1.0 in one circuit. At 8000 cycles, coil C2 will supply about 0.53 of its maximum current and coil Cl will supply about 0.20 of its maximum current. The current of coil C2 will now have a 60 degree lead but the current of coil Cl will lag about degrees so that the two currents will add at about a 40 degree phase angle and the resultant current will be 0.53+0.20 cos 40 degrees or about 0.68 of the maximum of one circuit. This time the electromotive force produced in the'winding 36 of the transformer T will have the relative value equal to that of a current of 0.68. At 8200 cycles, the current flowing in each circuit will be roughly 0.30 of the maximum resonant value, the current supplied by the coil C2 leading by about '73 degrees and. the current supplied by the coil Cl lagging at about the same angle. These two currents will add at approximately 34 degrees phase angle and their resultant value will be 2x030 cos 1'7 degrees or about 0.57 of the;maximum resonant value of one circuit, and the resultant electromotive force induced in the winding 36 will have the relative value of 0.57. At 8400 cycles, the value of the resultant current will be substantially the same as at 8000 cycles, that is, about 0.68 of the maximum resonant value of one circuit. At 8600 cycles, the circuit including the coil Cl is resonant and its current fiow will be approximately the maximum value of 1.0 while the current for the coil C2 will be relatively small and the two currents will be nearly in quadrature. At 8800 cycles, which is the upper edge of the voice spectrum, the resultant current will have a value substantially the same as at 7600 cycles, namely, 0.45 of the resonant value of one circuit. Thus, at the three frequencies 8400, 8600 and 8800 cycles, the electromotive force induced in the winding 36 will have the relative value of 0.68, 1.0 and 0.45, respectively.

It should be noted that the reactance of one circuit on another will be at the tuning points equivalent to putting about eight times the impedance of the load in shunt, and at points other than the tuning points it will be equivalent to about four times the load impedance in shunt. Hence, the above resultant currents should be reduced about one twenty-fourth to one eighth of the value given. In Fig. 2 curve A is the approximate current-frequency characteristic of the resultant current of these two pick-up circuits of 3.25% power factor, staggered tuning and reversed connection. It will be noted from curve A that a 1 to 2 ratio in the current strength between the band edge frequencies and the midfrequencies is substantially obtained for the band extending from 7600 to 8800 cycles. In other words, these two pick-up circuits of Fig. 1 are operative to produce effects on the receiving apparatus the variation in the strength of which for the band edge frequencies and that for the mid-frequencies is well within the limits required for readily intelligible speech. It should be noted also that the 3.25% power factor circuits are many times sharper in tuning than can be used when a single pick-up circuit is employed for a given voice spectrum with the result that noise during communication periods will be materially reduced at the pick-up circuits and a comparatively simple filter only will be required.

Curve B of Fig; 2 is the current-frequency characteristic curve for the pick-up circuits of Fig. 1 when the coils Cl and C2 are included in 1.0% power factor circuits tuned to resonance at the calling frequency. It will be noted from this curve B that an 80 cycle variation either side of the resonance frequency of 7800 cycles will result in about one-half current strength. That is, during calling and code communication a 1 to 2 ratio of the resultant current strength is confined within a band cycles Wide and hence noise and unwanted energy will be suppressed to a low level, especially in viewof the fact, as stated previously, noise currents occur at the lower frequencies.

Coils Cl and C2 may also be used for supplying energy to the trafiic rails and the other parallel conductors by switching these coils from the receiving apparatus to the transmitting apparatus. As pointed out earier in the description, the output of the transmitting apparatus TA is connected with the winding Id of the transformer T over wires l2 and i3, a front contact 5960 of the directional relay DR being interposed in the wire I 2. It is clear that with the directional relay DR energized the winding 36 of the transformer T is disconnected from the receiving apparatus RA while the winding Id of that transformeris connected with the transmitting apparatus TA at the front contact 59-60. Consequently, with relay DR picked up and current supplied to the winding 14 electromotive forces of corresponding frequencies will be induced in the two windings 28 and 32 which in turn will cause current to flow in the coils Cl and C2 and electromotive forces of corresponding frequencies will be induced in the trafiic rails.

The operation of the apparatus may be described as follows: During non-communicating periods the microphone M will be placed in the rack and the handle IE will be set at the normal position. Under this condition both relays R and DR will be released and the two coils Cl and C2 will be included in 1.0% power factor circuits tuned to resonance at 7800 cycles and the connection of the two coils with the windings 28 and 32 will be in phase relationship. Hence, noise currents of only a few cycles will be picked up'and noise at the loud-speaker will be suppressed. Under this normal condition of the handle l5 reception of an impulse of calling current at 7800 cycles will be picked up and applied to the receiving apparatus with the result that a corresponding tone will be sounded at the loudspeaker. The coils CI and C2 will operate at high pick-up sensitivity and the circuit connection between the transformer T and the receiving apparatus will permit a relatively high energy transfer. Code impulses will likewise be received in the same manner with corresponding code notes sounding at the loud-speaker. To carry on a telephone conversation the handle [5 will be moved to the communicating position and i the microphone will be removed from the rack,

the contact 202l being now closed to pick up the tuning relay R. Relay R on picking up will transfer the coils Cl and C2 into the 3.25% power speaker. When the operator desires to senda tuning relay R. plied to the traffic rails by operating the handle telephone current, he will depress thefpush button l1 and pick up the directional relay DR, transferring the coils Cl and C2 from the receiving apparatus to the transmitting apparatus. To

receive a telephone current without. removal of the microphone from the rack the operator will hold the push button 24. depressed to pick up the A calling current will be sup- IE to the calling position to pick up the directional relay DR over the No. 3 position of the contact [6, and to render the calling means within the apparatusTA active by completing the connection between the wires 62 and 63 at the No. 3 position of the contact 6|. Code impulses will be sent by the operator moving the handle 1 [5 to the calling position for long and short ining from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

.1. In combination with railway train-carried telephone receiving apparatus including a loudspeaker for reproducing the audio frequencies of a telephone current, a first and a second low power factor inductor on a vehicle of the train for inductively'receiving electromotive forces due to a telephone current which flows in a conductor parallel to the train, a first circuit means for connecting the first inductor with the input of the receiving apparatus including capacitance for tuning the'circuit means to resonance at a first given voice frequency, and a second circuit capacitance for tuning the circuit means to resonance at a second given voice frequency, and said firSt'and second inductors reversed with respect to'one another in their influence on the receiving means for connecting the second inductor with the input of the receiving apparatus including apparatus.

'2.'In combination with railway train-carried telephone receiving apparatus adaptable of re- 'producing the audio frequencies of a-telephone current, a first and a second air core inductor coilwith a second winding of the transformer including a condenser for tuning that circuit to coil on the train electrically coupled with the traffic rails, a transformer, a first circuit for connecting the first coil with a first winding of the transformer including a condenser for tuning the circuit to resonance at a first given voice frequency, a second circuit for connecting the second resonance at a second given voice frequency, said first and second inductor coils connected with said respective windings reversed with reference to one another, and a. third circuit on the train connected with the input of the receiving apparatus including a third winding of the transformer.

3. In combination with railway train-carried telephone receiving apparatus including a loudspe aker operative to reproduce the audio frequencies of va carrier telephone current, two air .core inductor coils each mounted on the train to-link a magnetic field due to a carrier telephone :current flowing in thetrafiic rails in parallel, a transformer, a first circuit for connecting one of said coils with a first winding of the transformer including capacitance for tuning the circuit to resonanceat a frequency. relatively. close to the lowervedge of the voice spectrum of such carrier telephone current, a second circuit for connecting the second one of said coils with a second winding of the transformer including capacitance for tuning that circuit to resonance at a frequency 2 relatively close to the upper edge of the voice spectrum, said circuits connected with said windings reversed with respect to one another, and a third circuit on the train connected with the input of the receiving apparatus including a third: winding of the transformer. I

4. In' combination with railway train-carried telephone receiving apparatus including a5-loudspeaker, a firstand a second inductor-on the train electrically coupled with the trafiic rails, arelaytl5 a first circuit for each of said inductorcoils each including a back contact of the relay and each tuned to resonance at a givenvoice frequency, a second circuit for each of said inductor coils each includinga front contact ofthe relay andczo said second circuits tuned to resonance at difierent voice frequencies, circuit means connected with the input of the receiving apparatus effectively influenced by both of said first circuits and 'by both of said second circuits, and-manually:

controlled means for governing-said relay.

5. In combination with railway train-carried telephone receiving apparatus including a loudspeaker, a first and a second inductor coil on the train electrically coupled with the trafhc rails, a1

, having a back contact interposed in each of then,

calling'circuits and a front contact interposed in each of the telephone circuits, manually controlled means for governing'the relay, and circuit means connected-with the input of the receiving apparatus effectively influenced by each callingr; circuit and by each telephone circuit whereby the two inductor coils are tuned sharply to the same frequency for sounding-a calling tone at the loud-speaker in response to a calling current of said given voice frequency inductively received from the rails and which coils have their tuning staggered for reproducing at the loudspeaker the speech of a telephone current inductively received from the rails.

6. In combination with telephone-receiving ap -:1 paratus including a demodulator and a loudspeaker operative to reproduce the audio frequencies of a side band carrier telephone current, a plurality of air core windings electrically coupled with a communication channel eifective to transmit such telephone current, .a first circuit for each of said windings including capacitance and reactance for tuning the circuit to resonance at a predetermined side band frequency of the carrier Within the voice frequency range and for establishing a relatively low circuit power factor, said first circuits all tuned to the same frequency, a second circuit for each of said windings including capacitance and reactance for tuning the circuit to resonance at a given fre said second circuits having staggered tuning; circuit controlling contacts interposed in said first and second circuits andoperative to render either the first circuits all active or to render thesecond circuits all active, manually'controlledmeans for governing said contacts, and circuit means connected with the input of the receiving apparatus effectively influenced by all of said first and second circuits for causing the loud-speaker to- -sound a tone in response to a calling current of the predetermined frequency picked up from the channel and to reproduce the message of a side band carrier telephone current picked up.

'7. In combination with telephone receiving apparatus including a demodulator and a loudspeaker operative to reproduce the audio frequencies of a side band carrier telephone current, a first and a second air core low powerv factor coil each electrically coupled with a communication channel effective to transmit such telephone current, a first circuit for each of said coils including a condenser and each circuit tuned to resonance at a predetermined side band frequency of the carrier within the voice frequency range, a second circuit for each coil including a condenser and the tuning of the two circuits staggered at difierent side band frequencies of the carrier within the voice frequency range, circuit controlling contacts interposed in said first and second circuits operative to render either the first circuits or the second circuits active, manually controlled means for governing said contacts, and circuit means connected with the input of the receiving apparatus effectively influenced by both of said first circuits and by both of said second circuits whereby the loud-speaker will sound a tone in response to a calling current of said predetermined frequency picked up from the channel and will sound the audio frequencies of a side band carrier telephone current picked up from the channel.

8. In combination with railway train-carried telephone receiving apparatus capable of reproducing the audio frequencies of a telephone current, a band-pass filter including a reactor, a relay, an air core inductor coil on the train electrically coupled with the trafiic rails, a first circuit for said coil having capacitance and reactance for sharply tuning the circuit to resonance at a predetermined voice frequency at a relatively low power factor and said circuit including a back contact of the relay, a second circuit for said coil having capacitance and reactance for tuning the circuit to resonance at a given voice frequency at a relatively high power factor and said circuit including a front contact of the relay; a third train-carried circuit including a winding effectively influenced by said first and second circuits, said reactor of the filter and a back contact of the relay; a fourth traincarried circuit including said winding, the full filter and a front contact of the relay; manually controlled means for governing the relay, and means for connecting said filter reactor with the input of the receiving apparatus.

9. In train-carried communication equipment comprising receiving apparatus including a demodulator and a loud-speaker; and transmitting apparatus including a generator of carrier current, a microphone for modulating the carrier with voice frequencies and a means for generating a calling current having a frequency equal to the carrier modulated by a predetermined vcice frequency; in combination with the above instrumentalities an air core low power factor coil on the train electrically coupled with the trafiic rails, a tuning relay and a directional relay, a transformer, a first circuit for said coil,

including a winding of the transformer and a former winding and a front contact of the tuning relay and tuned broadly to pass the telephone current, a third circuit connected with the input of the receiving apparatus and including a second winding of the transformer and a back contact of the directional relay, a fourth circuit connected with the output of the transmitting apparatus and including a third winding of the transformer and a front contact of the directional relay; and manually controlled means operative to deenergize both of said relays to receive a calling current, to energize the tuning relay and release the directional relay for receiving a telephone current, to energize the directional relay and release the tuning relay for sending a calling current and to energize both of said relays for sending a telephone current.

10. In train-carried communication equipment comprising receiving apparatus including a demodulator and a loud-speaker; and transmitting apparatus including a generator of carrier current, a microphone for modulating the carrier with voice frequencies and a means for generating a calling current having a frequency equal to the carrier modulated by a predetermined voice frequency; in combination with the above instrumentalities a pair of air core coils mounted on the train each electrically coupled with a conductor parallel with the train, a first circuit for each coil each tuned sharply to resonance at the calling current frequency, a second circuit for each coil each tuned broadly to a given frequency within the voice band of the modulated carrier, said second circuits being tuned to different frequencies, means including contacts of a circuit controller for coupling said first circuits to either the receiving apparatus or to the transmitting apparatus with said coils in phase with respect to each other, and other means including contacts of the circuit controller for coupling said second circuits with either the receiving apparatus or the transmitting apparatus with said coils reversed in phase with respect to each other.

11. In combination with railway train-carried telephone receiving apparatus capable of reproducing the audio frequencies of a telephone current, a band-pass filter including reactors and condensers and effective to pass the frequencies of said telephone current and to substantially exclude all other frequencies, an inductor on the train for inductively receiving such telephone current, a relay, a first circuit for said inductor having capacitance and reactance for sharply tuning the circuit to resonance at a predetermined frequency of such telephone current and said circuit including a back contact of said relay, a second circuit for said inductor having capacitance and reactance for tuning said circuit broadly to voice range of frequencies of said current and said second circuit including a front contact of the relay, a winding effectively influenced by said first and second circuits; a third circuit including said winding, a back contact of the relay and a particular reactor and condenser of the filter, said third circuit tuned to pass said predetermined frequency only; a fourth circuit including said winding, a front contact of the relay and the full filter; means for governing said relay, and other means to connect the output of the filter with the receiving apparatus.

i8 aci -19s i2. Inccmbination with railway trainecarried cf said relay and a, particular condenser and "telephonereceiving apparatus capable of reproreact,0-r ;.of said filter, saidpircuit meanstuned ducing;the endicfrequencies of a telephonecursherply cto passe predetermined frequency .Qf (rent, a band-pass filter including reactorsand such telephone current only; another circuit .egndensers and effective topass the frequencies -me a ns on the train including the inductor, a, ;5 of said telephone currentand to substantially front contact of the relay and the full filter; giexclujde other frequencies, an inductor 0n the vmeans forgovermng said relay, and other means train for 1 ind uctive1y receiving such telephone ;to connect thecutput of the filter with said recurrent, ,a :relay; Va "first train-carried circuit ceivingapparatus. 1p.,.mea,ns1inc1uding said inductor, a, back contact PAUL N. BOSSART. ;1 0 

